Oklahoma is debating the delay of three executions while the U.S. Supreme Court reviews the kind of sedative used for lethal injections.

It comes after a number of death row inmates suffered reactions to the drug or were not rendered sufficiently unconscious.

Rather than stop the executions himself, Oklahoma Attorney General Scott Pruitt took the unusual step of asking the justices for a stay.

The review will test the sedative - midazolam - to check that it renders recipients unconscious, the state's attorney general said in a Monday filing with the court.

Delayed? Richard Glossip, 52, who arranged for his employer to be beaten to death, may not be executed this Thursday as the Supreme Court reviews the sedative used in lethal injections by Oklahoma state

Also put on hold: John Grant, 53, (left) is scheduled to die on February 19 for stabbing a correction worker to death, and Benjamin Cole, 49, (right) who killed his nine-month-old daughter, is due to die on March 5

Oklahoma wants the right to resume executions if it finds a different suitable drug.

The delay would affect inmate Richard Glossip, 52, who was convicted of arranging for 'the beating death of his employer'; John Grant, 53, who 'stabbed a correction worker to death'; and Benjamin Cole, 49, who 'bent his nine-month-old daughter in half, breaking her spine, killing her.'

Glossip is scheduled to be executed on Thursday.

Grant's execution is set for February 19 and Cole is scheduled to be put to death March 5.

They are among four death row inmates who sued the state, saying they fear the sedative midazolam cannot prevent their suffering as lethal drugs take effect.

HOW LETHAL INJECTIONS WORK

States that have the death penalty execute convicts using three drugs.

The first sedates the inmate, the second paralyzes, and the third stops their heart.

Oklahoma adopted midazolam in 2013, which is also used in Florida.

The first execution using midazolam was called off after the convict, murderer Clayton Lockett, clenched his teeth, moaned and writhed on the gurney before a doctor noticed a problem with the intravenous line.

One of the four was executed this month and showed no signs of physical distress.

Charles Warner implied discomfort during his final statement January 15 but before any lethal drugs were administered.

'It is important that we act in order to best serve the interests of the victims of these horrific crimes and the state's obligation to ensure justice in each and every case,' Pruitt said in a statement.

'The families of the victims in these three cases have waited a combined 48 years for the sentences of these heinous crimes to be carried out.'

Oklahoma, as well as Florida, uses midazolam as one of three drugs in lethal injection executions.

The second drug serves to paralyze the inmate and the third one is used to stop his heart.

Last April, Oklahoma used midazolam for the first time in the execution of death row inmate Clayton Lockett, who clenched his teeth, moaned and writhed on the gurney before a doctor noticed a problem with the intravenous line and the execution was called off.